Crystalline GeSn thin films with Sn content up to 0.28 were deposited on Sn graded GeSn buffer on a Ge substrate at low temperatures by sputtering epitaxy. The structural properties of the high-Sn content GeSn alloy films were characterized by high resolution transmission electron microscopy and X-ray diffraction. The effect of annealing on the segregation of Sn in the high-Sn content GeSn film was investigated, and both the Ge0.72Sn0.28 and the Ge0.8Sn0.2 ilms were found to be stable after annealing at temperatures below 400 degrees(degrees), which meets the needs of thermal budget for future photonic devices fabrication. The present results indicate that sputtering epitaxy is cost-effective method for growing high-Sn GeSn films. (C)2018 Elsevier B.V. All rights reserved.